CN114450906B - Network access node and client device for adaptive DMRS mode - Google Patents

Abstract

The present invention relates to a network access node and a client device for adaptive DMRS. The network access node (100) sends a DMRS to a client device (300) according to a first DMRS pattern in a wireless channel, and when it is determined that the delay spread of the wireless channel exceeds the cyclic prefix length of the first DMRS pattern, a second DMRS pattern formed by the first DMRS pattern is obtained, and the second DMRS pattern has one or more empty resource units associated with the DMRS. Thereafter, the network access node sends a DMRS to the client device (300) according to the second DMRS pattern. Thus, when the delay spread of the wireless channel exceeds the cyclic prefix length, a more robust DMRS pattern can be provided. Therefore, channel estimation can be improved. In addition, the present invention also relates to corresponding methods and computer programs.

Description

Network access node and client device for adaptive DMRS mode

Technical Field

The present invention relates to a network access node and a client device for an adaptive DMRS mode. In addition, the present invention also relates to a corresponding method and a computer program.

Background technique

In 3GPP new radio (NR), multiple parameter sets are supported, and the relationship between subcarrier spacing (SCS) and cyclic prefix (CP) types is shown in TS38.211f40. In orthogonal frequency division multiplexing (OFDM) systems, in order to reduce inter-symbol interference (ISI) and inter-carrier interference (ICI), the CP length must be long enough to cover the maximum delay spread of the wireless channel. In addition, it has been observed that the channel delay in non-line-of-sight (NLOS) environments is much longer than that in line-of-sight (LOS) environments. In NR, the extended CP only supports 60kHz SCS. Therefore, when using a large parameter set with a large SCS, the CP length may not be enough, and the mechanism for handling excessive channel delay spread is very important in NR evolution.

In NR, CP-type is a cell-specific parameter, which means that if the CP-length in one cell changes, the change applies to all user equipment (UE) located in the same cell. This design is inflexible because some UEs far away from the gNB experience longer latency than those close to the gNB. To improve the connectivity of these cell-edge UEs, it is better to configure a longer CP, but this increases the system overhead and leads to reduced spectral efficiency.

When the CP length is not enough, strong ISI and ICI will occur and destroy the orthogonality between subcarriers. An exemplary scenario is a high-speed train with a large Doppler frequency, where strong ICI may occur. ICI and/or ISI can create error floors for bit-error-rate (BER) and block-error-rate (BLER). Although advanced receivers such as time-domain channel shortening (CS) or iterative interference cancellation (IC) receivers can be applied, these receivers require accurate channel estimation (CE). Due to the superposition of ISI and/or ICI, channel estimation based on wideband reference signals (such as demodulation reference signal (DMRS) or phase tracking reference signal (PTRS)) may be inaccurate and degrade the performance of these advanced receivers. In addition, inaccurate channel estimation can also lead to potential problems in power-delay-profile (PDP) estimation or filter design for channel estimation denoising.

In NR Rel.15, two configuration types of DMRS patterns are specified for downlink (DL) and uplink (UL) DMRS. DMRS configuration type 1 uses an interleaved frequency domain multiple access (IFDMA)-based approach intended for scenarios with up to 8 orthogonal ports, while configuration type 2 uses a 2-frequency division orthogonal cover code (2-FD-OCC) intended for scenarios with up to 12 orthogonal ports. The DMRS patterns for PDSCH are described in detail in Section 7.4.1.1.2 and mapped to physical resources in TS 38.211f40. For DMRS configuration type 1, the DMRS port index for CP-OFDM dual-symbol DMRS and the DMRS port index in the code division multiplexing (CDM) group are {0,1,4,5} and {2,3,6,7}. For DMRS configuration type 2, the DMRS port indexes in the CDM group are {0,1,6,7}, {2,3,8,9}, and {4,5,10,11}.

Summary of the invention

An object of embodiments of the present invention is to provide a solution to reduce or solve the disadvantages and problems of conventional solutions.

The above and other objects are achieved by the subject-matter of the independent claims. Further advantageous embodiments of the invention can be found in the dependent claims.

According to a first aspect of the present invention, the above and other objects are achieved by a network access node for a wireless communication system, the network access node being configured to:

Sending a demodulation reference signal (DMRS) to a client device according to a first demodulation reference signal (DMRS) pattern in a wireless channel;

When it is determined that the delay spread of the wireless channel exceeds the cyclic prefix length of the first DMRS pattern, obtaining a second DMRS pattern formed by the first DMRS pattern, the second DMRS pattern having one or more empty resource units associated with the DMRS;

The DMRS is sent to the client device according to the second DMRS pattern.

The advantage of the network access node according to the first aspect is that by blanking out the DMRS pattern to adapt to excessive delay spread, a more robust solution is provided than conventional solutions. This also means that both ICI and ISI are reduced, thereby improving channel estimation. With improved channel estimation, advanced receivers can perform better on the receiver side (i.e., on the client device).

In one implementation of the network access node according to the first aspect, transmission is not scheduled on empty resource elements of the second DMRS pattern.

The advantage of this implementation is that ISI and/or ICI can be reduced when the CP is insufficient. In addition, the enhanced channel estimation algorithm can be used to obtain accurate channel estimation using DMRS according to the blanking pattern.

In an implementation manner of the network access node according to the first aspect, a DMRS pattern of the second DMRS pattern forms a comb structure.

In some cases, the second DMRS pattern may form a comb structure having a sparse property.

The advantage of this implementation is that the comb structure can be applied to the current NR standard. The comb structure is obtained by applying the blanking, which is equivalent to adding the SCS of the DMRS symbol. Therefore, the improved decoding process can also be applied in the client device.

In an implementation manner of the network access node according to the first aspect, the second DMRS pattern is DMRS configuration type 1, and wherein resource elements of antenna ports 0/1/4/5 or antenna ports 2/3/6/7 are set to null.

The advantage of this implementation is that it is compatible with the current NR standard.

In an implementation manner of the network access node according to the first aspect, the second DMRS pattern is DMRS configuration type 2, and wherein at least resource elements of antenna ports 0/1/6/7, 2/3/8/9 or 4/5/10/11 are blanked.

The advantage of this implementation is that it is compatible with the current NR standard.

In an implementation manner of the network access node according to the first aspect, the network access node is further configured to:

When it is determined that the delay spread of the wireless channel exceeds the cyclic prefix length, the transmission of the DMRS according to the second DMRS pattern is adapted to at least one of a parameter set, a subcarrier spacing, and a wireless access technology.

One advantage of this implementation is that further measures can be taken to combat excessive delay spread, thereby further reducing the negative impact of excessive delay spread.

In an implementation manner of the network access node according to the first aspect, determining that the delay spread of the wireless channel exceeds the cyclic prefix length includes:

A first control message is received from a client device, wherein the first control message indicates that a delay spread of a wireless channel exceeds a cyclic prefix length.

The advantage of this implementation is that the client device directly informs the network access node through control signaling of excessive delay spread. Since the client device acts as a receiver, the client device can perform accurate channel performance.

In an implementation of the network access node according to the first aspect, the first control message is received in a physical uplink control channel (PUCCH), a medium access control control element (MAC-CE) or a radio resource control (RRC) signaling.

The advantage of this implementation is that conventional control signaling procedures can be used, which means that the complexity is reduced when implementing the solution.

In an implementation manner of the network access node according to the first aspect, the network access node is further configured to:

A second control message is sent to the client device, wherein the second control message indicates that the DMRS is to be transmitted according to a second DMRS pattern.

The advantage of this implementation is that the client device is informed of the change of the DMRS pattern through control signaling. Therefore, the client device does not have to blindly decode the received DMRS to know that the DMRS pattern has changed. This means that although the decoding complexity is reduced, the payload is higher.

In an implementation manner of the network access node according to the first aspect, the second control message is sent in a physical downlink control channel (PDCCH), MAC-CE or RRC signaling.

The advantage of this implementation is that conventional control signaling procedures can be used, which means that the complexity is reduced when implementing the solution.

In an implementation manner of the network access node according to the first aspect, the second control message is an indication bit, wherein a "1" value of the indication bit indicates that the DMRS is transmitted according to the second DMRS pattern, and a "0" value of the indication bit indicates that the DMRS is transmitted according to the first DMRS pattern.

The advantage of this implementation is that only 1 bit of information is sent to the client device to notify the change of the DMRS pattern, which generates very little payload in the system.

According to a second aspect of the present invention, the above and other objects are achieved by a client device for a wireless communication system, the client device being configured to:

receiving a DMRS from a network access node according to a first DMRS pattern in a wireless channel;

When determining that the delay spread of the wireless channel exceeds the cyclic prefix length of the first DMRS pattern, sending a first control message to the network access node, wherein the first control message indicates that the delay spread of the wireless channel exceeds the cyclic prefix length;

receiving a second control message from the network access node, wherein the second control message indicates transmission of a DMRS according to a second DMRS pattern, wherein the second DMRS pattern is formed by the first DMRS pattern, the second DMRS pattern having one or more empty resource elements associated with the DMRS;

A DMRS is received from a network access node according to a second DMRS pattern.

The advantage of the client device according to the second aspect is that by blanking out the DMRS pattern to adapt to excessive delay spread, a more robust solution is provided than conventional solutions. This also means that ICI and/or ISI are reduced, thereby improving channel estimation. With improved channel estimation, the advanced receiver can perform better on the receiver side (i.e., on the client device).

In an implementation of the client device according to the second aspect, no transmission is scheduled on empty resource elements of the second DMRS pattern.

One advantage of this implementation is that ISI and ICI can be reduced when the required CP is insufficient. In addition, an enhanced channel estimation algorithm can be used to obtain accurate channel estimation based on DMRS according to a detailed blanking pattern.

In an implementation manner of the client device according to the second aspect, the DMRS pattern of the second DMRS pattern forms a comb structure.

The advantage of this implementation is that the comb structure can be applied to the current NR standard. The comb structure is obtained by applying the blanking, which is equivalent to adding the SCS of the DMRS symbol. Therefore, the improved decoding process can also be applied in the client device.

In an implementation manner of the client device according to the second aspect, the second DMRS mode is DMRS configuration type 1, and resource elements of antenna ports 0/1/4/5 or antenna ports 2/3/6/7 are set to blank.

The advantage of this implementation is that it is compatible with the current NR standard.

In an implementation manner of the client device according to the second aspect, the second DMRS pattern is a DMRS configuration type 2, wherein at least resource elements of antenna ports 0/1/6/7, 2/3/8/9 or 4/5/10/11 are blanked.

The advantage of this implementation is that it is compatible with the current NR standard.

According to the second aspect, in an implementation manner of the client device, the first control message is sent in PUCCH, MAC-CE or RRC signaling.

The advantage of this implementation is that conventional control signaling procedures can be used, which means that the complexity is reduced when implementing the solution.

In an implementation manner of the client device according to the second aspect, the second control message is received in PDCCH, MAC-CE or RRC signaling.

The advantage of this implementation is that conventional control signaling procedures can be used, which means that the complexity is reduced when implementing the solution.

In an implementation manner of the client device according to the second aspect, the second control message is an indication bit, wherein "1" of the indication bit indicates that the DMRS is transmitted according to the second DMRS pattern, and "0" of the indication bit indicates that the DMRS is transmitted according to the first DMRS pattern.

The advantage of this implementation is that only 1 bit of information is sent to the client device to notify the change of the DMRS pattern, which generates very little payload in the system.

According to a third aspect of the present invention, the above and other objects are achieved by a method for a network access node, the method comprising:

Sending a demodulation reference signal (DMRS) to a client device according to a first demodulation reference signal (DMRS) pattern in a wireless channel;

When it is determined that the delay spread of the wireless channel exceeds the cyclic prefix length of the first DMRS pattern, obtaining a second DMRS pattern formed by the first DMRS pattern, the second DMRS pattern having one or more empty resource units associated with the DMRS;

The DMRS is sent to the client device according to the second DMRS pattern.

The method according to the third aspect can be extended to an implementation corresponding to the implementation of the network access node according to the first aspect. Therefore, the implementation of the method comprises the features of the corresponding implementation of the network access node.

The advantages of the method according to the third aspect are the same as the advantages of the corresponding implementation of the network access node according to the first aspect.

According to a fourth aspect of the present invention, the above and other objects are achieved by a method for a client device, the method comprising:

receiving a DMRS from a network access node according to a first DMRS pattern in a wireless channel;

When determining that the delay spread of the wireless channel exceeds the cyclic prefix length of the first DMRS pattern, sending a first control message to the network access node, wherein the first control message indicates that the delay spread of the wireless channel exceeds the cyclic prefix length;

receiving a second control message from the network access node, wherein the second control message indicates transmission of a DMRS according to a second DMRS pattern, wherein the second DMRS pattern is formed by the first DMRS pattern, the second DMRS pattern having one or more empty resource elements associated with the DMRS;

A DMRS is received from a network access node according to a second DMRS pattern.

The method according to the fourth aspect can be extended to an implementation corresponding to the implementation of the client device according to the second aspect. Therefore, the implementation of the method includes one or more features of the corresponding implementation of the client device.

The advantages of the method according to the fourth aspect are the same as the advantages of the corresponding implementation of the client device according to the second aspect.

The present invention also relates to a computer program, characterized in that the program code, when executed by at least one processor, causes the at least one processor to perform any method according to an embodiment of the present invention. In addition, the present invention also relates to a computer program product, comprising a computer-readable medium and a computer program, wherein the computer program is included in the computer-readable medium and comprises one or more of the following group: read-only memory (ROM), programmable ROM (PROM), erasable PROM (EPROM), flash memory, electrically EPROM (EEPROM) and hard disk drive.

Other applications and advantages of embodiments of the present invention will be apparent from the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are intended to illustrate and explain different embodiments of the present invention, in which:

- FIG1 shows a network access node according to an embodiment of the present invention;

- FIG. 2 shows a flow chart of a method for a network access node according to an embodiment of the present invention;

- Figure 3 shows a client device according to an embodiment of the present invention;

- FIG. 4 shows a flow chart of a method for a client device according to an embodiment of the present invention;

- FIG5 shows a wireless communication system according to an embodiment of the present invention;

- FIG. 6 shows the blanking of DMRS according to an embodiment of the present invention;

- Figure 7 shows a signalling scheme according to an embodiment of the present invention;

- Figure 8 shows a signalling scheme according to an embodiment of the present invention;

- Figure 9 shows a signalling scheme according to an embodiment of the present invention;

- Figures 10a-10c illustrate processing at a client device according to an embodiment of the present invention; and

- Figure 11 shows a flow chart of a processing method for a client device according to an embodiment of the present invention.

Detailed ways

As described above, in NR, extended CP is only used for 60kHz SCS. For other parameter sets, only the adjusted normal CP is supported, which may not be enough when the channel delay spread is too large. When the channel delay is too large (i.e., greater than the configured CP), the channel estimation accuracy will be affected by strong ISI and ICI, which may require reduced throughput and increased complexity of advanced receivers to reduce interference.

The inventors have noted that in NR, the robust DMRS transmission mode through DCI format 1_0 and some advanced DMRS modes in DMRS configuration 1 scheduled by DCI format 1_1 can be used to enhance channel estimation on the UE side to combat excessive delay spread of the wireless channel. In NR, for DCI format 1_0, the UE assumes that a single symbol pre-DMRS of configuration type 1 is sent on DMRS port 1000, and assumes that all remaining orthogonal antenna ports are not related to transmitting a physical downlink shared channel (PDSCH) to another UE. For DCI format 1_1, antenna port indications for single user MIMO (SU-MIMO) and multi user MIMO (MU-MIMO) support advanced multiple input multiple output (MIMO) schemes. Antenna port – 4, 5 or 6 bits as defined in Table 7.3.1.2.2-1/2/3/4, where the number of CDM groups with values 1, 2 and 3 without data refers to CDM groups {0}, {0,1}, {0,1,2} respectively. The antenna ports {p ₀ ,…p _v-1 } shall be determined according to the DMRS port order given in Table 7.3.1.2.2-1/2/3/4 of TS 38.214f40.

In addition, corresponding UE auxiliary signaling and network indication signaling can be proposed to notify the network and/or UE to adjust its MIMO scheme when an excessive delay spread scenario occurs. Therefore, the purpose of an embodiment of the present invention is to propose a network adaptation mechanism to enable a robust DMRS mode, for example, when the UE suffers from excessive channel delay spread. Even an adapted parameter set/carrier/radio access technology (RAT) can be applied. The purpose is to eliminate the impact of excessive channel delay spread, which is a display method of the adapted bandwidth part (BWP), carrier and/or radio access technology (RAT).

Specifically, in order to enable a robust DMRS mode, a DMRS configuration is enabled so that only a portion of REs in an OFDM symbol carry DMRS, wherein other REs are emptied, i.e., not used for transmission to the current UE or other UEs. This is an implicit method for eliminating the impact of excessive channel delay spread. For example, for a specific DMRS configuration, for example, in an OFDM symbol carrying DMRS, all odd-indexed REs are emptied, then in the time domain, the RS symbol can have two identical parts, the first part being like the CP of the second part. Based on these properties, a CE with good quality without ISI and ICI can be obtained in a scenario where the channel delay is too large. For an adapted robust DMRS mode sub-scheme, a corresponding enhanced channel estimation algorithm for UE to improve channel estimation is described. As described above, the quality of channel estimation is critical to the successful application of interference suppression or elimination receivers when decoding data channels. For the above reasons, the present disclosure proposes a scheme applicable to network access nodes, client devices, wireless communication systems, corresponding methods, and computer programs.

FIG1 shows a network access node 100 according to an embodiment of the present invention. In the embodiment shown in FIG1 , the network access node 100 includes a processor 102, a transceiver 104, and a memory 106. The processor 102 is coupled to the transceiver 104 and the memory 106 via a communication device 108 known in the art. The network access node 100 can be used for wireless communication and wired communication in a wireless communication system and a wired communication system, respectively. The wireless communication capability is provided by an antenna or antenna array 110 coupled to the transceiver 104, and the wired communication capability is provided by a wired communication interface 112 coupled to the transceiver 104. In the present disclosure, the network access node 100 is used to perform certain actions, which can be understood to mean that the network access node 100 includes appropriate devices for performing these actions, such as the processor 102 and the transceiver 104.

According to an embodiment of the present invention, the network access node 100 is used to send a DMRS to the client device 300 according to a first DMRS pattern in a wireless channel. The network access node 100 is also used to obtain a second DMRS pattern formed by the first DMRS pattern when it is determined that the delay spread of the wireless channel exceeds the cyclic prefix length of the first DMRS pattern, and the second DMRS pattern has one or more empty resource units associated with the DMRS. The network access node 100 is also used to send a DMRS to the client device 300 according to the second DMRS pattern.

FIG2 shows a flow chart of a corresponding method 200 that may be performed in a network access node 100 (e.g., the network access node shown in FIG1 ). The method 200 includes sending (202) a DMRS to a client device according to a first DMRS pattern in a wireless channel. The method 200 also includes obtaining a second DMRS pattern formed by the first DMRS pattern when it is determined (204) that the delay spread of the wireless channel exceeds a cyclic prefix length of the first DMRS pattern, the second DMRS pattern having one or more empty resource units associated with the DMRS. The method 200 also includes sending (206) a DMRS to the client device 300 according to the second DMRS pattern.

For example, the second DMRS can be obtained by leaving the orthogonal DMRS ports as empty subcarriers, not transmitting data to the client device 300, and not transmitting DMRS to another client device. Therefore, the first DMRS pattern is set to null in an appropriate manner to obtain the second DMRS pattern.

FIG3 shows a client device 300 according to an embodiment of the present invention. In the embodiment shown in FIG3 , the client device 300 includes a processor 302, a transceiver 304, and a memory 306. The processor 302 is coupled to the transceiver 304 and the memory 306 via a communication device 308 known in the art. The client device 300 also includes an antenna or antenna array 310 coupled to the transceiver 304, which means that the client device 300 is used for wireless communication in a wireless communication system. In the present disclosure, the client device 300 is used to perform certain actions, which can be understood to mean that the client device 300 includes appropriate devices for performing these actions, such as the processor 302 and the transceiver 304.

According to an embodiment of the present invention, the client device 300 is used to receive a DMRS from the network access node 100 according to a first DMRS pattern in a wireless channel. The client device 300 is also used to send a first control message 502 to the network access node 100 when it is determined that the delay spread of the wireless channel exceeds the cyclic prefix length of the first DMRS pattern. The first control message 502 indicates that the delay spread of the wireless channel exceeds the cyclic prefix length. The client device 300 is also used to receive a second control message 504 from the network access node 100. The second control message 504 indicates that the DMRS is transmitted according to the second DMRS pattern. The second DMRS pattern is formed by the first DMRS pattern, and the second DMRS pattern has one or more empty resource units associated with the DMRS. The client device 300 is also used to receive a DMRS from the network access node 100 according to the second DMRS pattern.

The client device 300 may determine that the delay spread of the wireless channel exceeds the cyclic prefix length of the first DMRS pattern using any method known in the art. For example, the client device 300 may determine the delay spread using a power delay profile (PDP) estimate of the channel. Another example is when the client device observes that the received signal suffers from strong ISI and/or ICI.

FIG4 shows a flow chart of a corresponding method 400 that may be performed in a client device 300 (e.g., the client device shown in FIG3 ). The method 400 includes receiving (402) a DMRS from a network access node 100 according to a first DMRS pattern in a wireless channel. The method 400 also includes sending a first control message 502 to the network access node 400 upon determining (404) that a delay spread of the wireless channel exceeds a cyclic prefix length of the first DMRS pattern. The first control message 502 indicates that the delay spread of the wireless channel exceeds the cyclic prefix length. The method 400 also includes receiving (406) a second control message 504 from the network access node 100. The second control message 504 indicates that a DMRS is transmitted according to a second DMRS pattern. The second DMRS pattern is formed by the first DMRS pattern, the second DMRS pattern having one or more empty resource units associated with the DMRS. The method 400 also includes receiving (408) a DMRS from the network access node 100 according to the second DMRS pattern.

FIG5 shows a wireless communication system 500 according to an embodiment of the present invention. The wireless communication system 500 includes a network access node 100 and a client device 300 for operating in the wireless communication system 500. For simplicity, the wireless communication system 500 shown in FIG5 includes only one network access node 100 and one client device 300. However, the wireless communication system 500 may include any number of network access nodes 100 and any number of client devices 300 without departing from the scope of the present invention. In the wireless communication system 500, the network access node 100 and the client device 300 are used to communicate with each other in a downlink (DL) and an uplink (UL) using conventional protocols and channels according to appropriate communication standards. For example, the wireless communication system 500 may be LTE, NR, or a multi-RAT system including more than one RAT.

In the following disclosure, further embodiments of the present invention are explained and described in the context of NR. Therefore, terms, concepts and system designs are used according to NR. In particular, the network access node 100 corresponds to the gNB 100 and the client device 300 corresponds to the UE 300. However, the embodiments of the present invention are not limited thereto and are only limited by the appended claims.

In some embodiments, due to the blanking of REs of the DMRS pattern according to the present invention, the gNB 100 transmits DMRS only on a portion of REs on the OFDM symbol corresponding to the DMRS transmission. A portion in this context means that transmission is performed on less than 100% of the REs. A portion can be given as a percentage (such as 50% and 25%) or a portion (such as 1/2 and 1/4). A special case is described that allows an enhanced channel estimation algorithm to combat excessive delay spread of the wireless channel. It should be noted that the gNB 100 is not limited to the transmission of a specific DMRS pattern, but can transmit any DMRS pattern including empty REs. However, the comb and sparse DMRS patterns described in Figure 6 have some specific advantages. In the DMRS pattern shown in Figure 6, all odd-indexed REs (or subcarriers) corresponding to the previous DMRS positions are blanked and do not carry data or DMRS or any other reference signal. That is, if the empty REs are to be allocated to another UE, the gNB 100 will reallocate these radio resources to other radio resources that are not empty resources. In another example, all even-indexed REs (or subcarriers) of the DMRS pattern may be blanked instead, but the channel estimation algorithm at the receiver side is changed accordingly.

In NR Rel.15, DMRS configuration type 1 is suitable for the construction of comb and sparse DMRS patterns according to embodiments of the present invention. In the existing antenna port indication table 7.3.1.2.2-1 shown below, all possible cases that support enhanced channel estimation are listed with the letter "Y" (i.e., YES), i.e., values 3, 4, and 7. For all these indicated cases, they share the same properties, namely: indicating antenna ports from a single CDM group; only port 0, port 1, port 4, and port 5 are applicable on even subcarriers; other orthogonal DMRS ports are reserved as empty subcarriers, and do not transmit data for the same UE or DMRS for another UE. It should be noted that values 12-15 in Table 7.3.1.2.2-1 are reserved, and only three configurations marked as "Y" support enhanced CE, which can be indicated using three reserved values.

Table 7.3.1.2.2-1: Antenna port (1000 + DMRS port), dmrs-Type = 1, maxLength = 1

For Table 7.3.1.2.2-2 (not shown), i.e., for DMRS type 1 and maxlength=2, values of 3, 4, 7, 12, 13, 16, 17, 20, 22, 24, 26 and 28 are suitable for DMRS patterns according to embodiments of the present invention.

It is also important to note that similar techniques can be applied to the DMRS of the physical uplink shared channel (PUSCH). However, since the UL transmission is completely controlled by the network scheduler, for example, the network implementation for uplink data scheduling is used to enable comb and sparse DMRS patterns in the UL.

In addition, in order for the gNB 100 to apply adjustments such as adapted BWP, carrier, RAT and/or DMRS antenna port configuration, the UE 300 may send a first control message 502 in the UL to notify that the channel delay of the wireless channel is too large. On the other hand, the gNB 100 may also detect the excessive delay spread on its own. For example, by uplink channel estimation in time-division-duplex (TDD) mode, or by detecting that the UE 300 is at the cell edge and making adjustments without signaling assistance from the UE 300. In both cases, the gNB 100 may adapt the DMRS transmission to counteract the effects of the excessive delay spread. Switching BWP, carrier or RAT to counteract the excessive delay spread is relatively easy, and conventional techniques may be employed. In contrast, in the following disclosure, details are provided to illustrate the DMRS pattern adaptation according to an embodiment of the present invention. To enable the robust DMRS pattern, the UE 300 may receive a second control message 504 indicating a specified DMRS pattern configuration from the gNB 100, or the UE 300 may blindly detect the DMRS pattern based on the received DMRS symbols. These different options at the gNB 100 and the UE 300 result in three embodiments of the present invention, including different signaling schemes introduced in the wireless communication system 500. Therefore, in order to enable network adaptation under excessive channel delay spread, three possible non-limiting embodiments for implementing a specified DMRS antenna port configuration at the gNB 100 are proposed herein.

In one embodiment shown in FIG7 , UE allocation signaling in the uplink and indication signaling in the downlink are required. The UE allocation signaling in the uplink indicates that the channel delay is too large, and the downlink indicator of the gNB 100 indicates the specified DMRS antenna port configuration. The embodiment shown in FIG7 includes the following steps:

I. UE 300 receives DMRS from gNB 100 according to a first DMRS pattern (not shown). UE 300 determines excessive channel delay spread of the wireless channel using any conventional method known in the art;

II. When the UE 300 determines that the channel delay spread is too large, it sends a first control message 502 indicating the excessive delay spread to the gNB 100. For example, the signaling can be performed in a physical uplink control channel (PUCCH) or in a higher layer signaling;

III. Upon receiving the first control message 502, the gNB 100 prepares to adapt the DMRS transmission to the UE 300;

IV. gNB 100 indicates the new DMRS transmission scheme, i.e., the second DMRS mode, to UE 300 via downlink control signaling in the form of a second control message 504;

V.UE 300 prepares to receive a new DMRS pattern according to the content of the second control message 504;

VI. gNB 100 adapts DMRS transmission to UE 300 according to the first control message 502, i.e., sends DMRS to UE 300 according to the second DMRS pattern including an empty RE represented by DMRS2 in the figure;

VII. The UE 300 applies the corresponding reception method/algorithm to the new DMRS pattern. The reception method at the UE 300 is explained in detail in the following disclosure.

In order to make the uplink report indicate the excessive delay spread to the gNB 100 (or the network), uplink control information similar to signaling, such as uplink control information (UCI), can be introduced for fast changing scenarios. If the excessive delay state changes slowly, higher layer signaling, such as medium access control (MAC) control element (CE) or radio resource control (RRC) signaling is more suitable for the indication of such excessive delay spread.

For downlink indication from gNB 100 (or network) to UE 300, the above mechanism can be implemented by introducing indication in the downlink control information (DCI) field in a fast changing scenario. If the excessive latency state changes slowly, higher layer signaling (such as MAC-CE or RRC signaling) is used instead to indicate the DMRS pattern information.

In the embodiment shown in FIG8 , only allocation signaling in the uplink is required. In the uplink signaling, the UE allocation signaling in the uplink indicates excessive channel delay, and the UE 300 then performs blind detection without receiving an indicator in the downlink from the gNB 100. The embodiment shown in FIG8 includes the following steps:

I. UE 300 receives DMRS from gNB 100 according to a first DMRS pattern (not shown). UE 300 determines that the channel delay spread of the wireless channel is too large;

II. UE 300 sends a first control message 502 indicating that the delay spread is too large to gNB 100 through uplink control signaling;

III. Upon receiving the first control message 502, the gNB 100 prepares to adapt the DMRS transmission to the UE 300;

IV. gNB 100 adapts DMRS transmission to UE 300 according to the first control message 502, i.e., sends DMRS according to the second DMRS pattern denoted as DMRS2 in the figure;

V.UE 300 applies blind detection to the received DMRS using a corresponding reception method according to the second DMRS pattern from gNB 100.

In the embodiment shown in FIG9 , the gNB 100 adjusts the DMRS antenna port configuration without receiving uplink information about excessive delay spread from the UE 300, but instead sends an indicator in the downlink to indicate the specified DMRS pattern configuration. The embodiment shown in FIG9 includes the following steps:

I. The gNB sends a DMRS to the UE 300 (not shown) according to the first DMRS pattern;

II.gNB 100 detects excessive delay spread of the radio channel;

III. gNB 100 indicates the new DMRS transmission scheme, i.e., the second DMRS mode, to UE 300 via downlink control signaling in the form of a second control message 504;

IV. UE 300 prepares to receive a new DMRS pattern according to the content of the second control message 504;

V.gNB 100 adapts to DMRS transmission to UE 300, i.e., sends DMRS to UE 300 according to a second DMRS pattern, which is represented as DMRS2 in the figure;

VI.UE 300 adapts the corresponding receiving method for the second DMRS mode.

In the following disclosure, two exemplary embodiments of a receiving method at UE 300 are described when the second DMRS pattern sent by gNB 100 has a comb and sparse structure.

Figures 10a-10c show a channel estimation algorithm at UE 300 to form N samples for fast Fourier transform (FFT). Figure 10a shows a time domain DMRS received in an OFDM symbol, where the channel delay spread is too large. Assuming that the CP length is L, the total channel delay is t+L, that is, the excessive channel delay spread on the CP is t, and therefore not greater than N/2. Due to the excessive channel delay spread, the first t samples are contaminated by ISI from the previously transmitted OFDM symbol. In Figures 10a-10c, in the first step I, corresponding to the CP and the excessive delay part, the t+L samples contaminated by ISI are removed, so only N-t samples that are not contaminated by ISI are taken. The processing result in step I is shown in Figure 10b. In the second step II of Figures 10a-10c, by using the same properties of the first N/2 part and the second N/2 part, the first t samples are copied from the second part and added to the front part, which produces N samples of full length, as shown in Figure 10c. Finally, an FFT operation of size N transfers the time domain DMRS shown in Figure 10c into the frequency domain and obtains a channel estimate without ISI or ICI. The only drawback of the method shown in Figures 10a-10c is that using the same t samples twice will result in a marginal diversity loss. However, when t<<N/2, the loss is not significant.

FIG11 shows a flow chart of the channel estimation algorithm of UE 300. In FIG11, two FFTs of size N/2 are performed on the time domain samples to obtain two channel estimates, and then the two channel estimates are combined to derive a combined channel estimate with higher accuracy, especially when t≈N/2. This is especially true when t≈N/2, because in this case, almost the entire first half is corrupted by ISI and should not be used for channel estimation before the interference of ISI is removed.

In step 602, after removing the CP, an FFT of size N/2 is performed on the second N/2 samples of the received time domain samples of the DMRS to restore the frequency domain DMRS samples.

In step 604, an initial channel estimate is obtained from the recovered frequency domain DMRS samples using the second N/2 time domain samples.

In step 606, after removing the CP, a corresponding N/2 size FFT is performed on the first N/2 samples of the received DMRS time domain samples to recover the frequency domain DMRS samples again (using ISI and/or ICI).

In step 608, the ISI and/or ICI of the first N/2 partial samples are reconstructed and then removed from the frequency domain DMRS samples recovered from the first N/2 time domain samples by cancellation in the time domain or frequency domain.

In step 610 , additional channel estimates are obtained based on the ISI and/or ICI-cancelled frequency domain samples of the first portion derived from step 608 .

In step 612, the initial channel estimate and the additional estimate are combined to obtain a combined channel estimate with improved accuracy.

It is contemplated that embodiments of the present invention may be implemented in suitable communication standards such as LTE and NR. The current scheme of how to implement DMRS configuration type 1 maxLength=1 and maxLength=1, respectively, has been described above. In addition, in this section, non-restrictive suggestions are made for specification changes to the DL excessive channel delay extension mode indicator in the DMRS physical layer for PDSCH in TS 38.212f40, where, for example, the following exemplary text portion may be added to indicate the use of a 1-bit excessive channel delay mode:

Mapping "1" indicates that when the UE is configured with DMRS configuration type 1 and the number of DMRS CDM groups without data is 2, other orthogonal DMRS ports are reserved as empty subcarriers and do not transmit data for the same UE or DMRS for another UE. Otherwise, mapping "0".

The client device 300 herein may be represented as a user device, user equipment (UE), mobile station, internet of things (IoT) device, sensor device, wireless terminal and/or mobile terminal, and may communicate wirelessly in a wireless communication system (sometimes also referred to as a cellular radio system). UE may also be referred to as a mobile phone, cellular phone, computer tablet or laptop with wireless capabilities. In this context, for example, UE may be a portable, pocket storage, handheld, computer-composed or vehicle-mounted mobile device capable of transmitting voice and/or data with other entities (e.g., other receivers or servers) via a wireless access network. UE may be a station (STA), which is any device including a media access control (MAC) and physical layer (PHY) interface to a wireless medium (WM) in accordance with IEEE 802.11. UE may also be used to communicate in 3GPP-related LTE and LTE-Advanced, in WiMAX and its evolution, and in fifth-generation wireless technologies (e.g., new air interfaces).

The network access node 100 in this article can also be represented as a wireless network access node, access network access node, access point or base station, such as a radio base station (RBS), which in some networks may be called a transmitter, "gNB", "gNodeB", "eNB", "eNodeB", "NodeB" or "B node" depending on the technology and terminology used. Depending on the transmission power and cell size, the wireless network access node can be of different categories, such as a macro eNodeB, a home eNodeB or a micro base station. The wireless network access node can be a station (STA), which is any device that includes an IEEE 802.11 standard media access control (MAC) and a physical layer (PHY) interface to a wireless medium (WM). The wireless network access node can also be a base station corresponding to a fifth generation (5G) wireless system.

In addition, any of the methods provided by the embodiments of the present invention can be implemented in a computer program having a codec module, and when a processing device runs the computer program, the computer program causes the processing device to perform the method steps. The computer program is included in a computer-readable medium of a computer program product. The computer-readable medium can basically include any memory, such as a read-only memory (ROM), a programmable read-only memory (PROM), an erasable PROM (EPROM), a flash memory, an electrically erasable PROM (EEPROM) or a hard disk drive.

In addition, those skilled in the art will appreciate that embodiments of the network access node 100 and the client device 300 include necessary communication capabilities in the form of functions, modules, units, elements, etc. for performing the scheme. Examples of other such devices, units, elements, and functions are: processors, memories, buffers, control logic, encoders, decoders, rate matchers, derate matchers, mapping units, multipliers, decision units, selection units, switches, interleavers, deinterleavers, modulators, demodulators, inputs, outputs, antennas, amplifiers, receiver units, transmitter units, DSPs, MSDs, TCM encoders, TCM decoders, power supply units, power feeds, communication interfaces, communication protocols, etc., which are appropriately arranged together to perform the scheme.

In particular, for example, one or more processors of the network access node 100 and the client device 300 may include one or more instances of a central processing unit (CPU), a processing unit, a processing circuit, a processor, an application specific integrated circuit (ASIC), a microprocessor, or other processing logic that can interpret and execute instructions. Therefore, the term "processor" may refer to a processing circuit that includes multiple processing circuits, for example, any, some, or all of the above-mentioned processing circuits. The processing circuit may also perform data processing functions for inputting, outputting, and processing data, including data buffering and device control functions, such as call processing control, user interface control, etc.

Finally, it should be understood that the present invention is not limited to the embodiments described above, but also relates to and incorporates all embodiments within the scope of the appended independent claims.

Claims (17)

1. A network access node (100) for a wireless communication system (500), the network access node (100) being configured to:

transmitting the DMRS to the client device (300) according to a first demodulation reference signal, DMRS, pattern in the wireless channel;

upon determining that the delay spread of the wireless channel exceeds the cyclic prefix length of the first DMRS pattern, obtaining a second DMRS pattern formed by the first DMRS pattern, the second DMRS pattern having one or more null resource elements associated with a DMRS, wherein transmissions are not scheduled on the null resource elements of the second DMRS pattern, the resource elements are nulled in OFDM symbols bearing the DMRS pattern, and the DMRS pattern of the second DMRS pattern forms a comb structure;

-transmitting DMRS to the client device (300) according to the second DMRS pattern.

2. The network access node (100) of claim 1, wherein the second DMRS pattern is DMRS configuration type 1, and wherein resource elements of antenna ports 0/1/4/5 or antenna ports 2/3/6/7 are nulled.

3. The network access node (100) of claim 1, wherein the second DMRS pattern is DMRS configuration type 2, and wherein at least the resource elements of antenna ports 0/1/6/7, 2/3/8/9, or 4/5/10/11 are nulled.

4. A network access node (100) according to any of claims 1-3, wherein determining that the delay spread of the wireless channel exceeds the cyclic prefix length comprises:

a first control message (502) is received from the client device (300), wherein the first control message (502) indicates that the delay spread of the wireless channel exceeds the cyclic prefix length.

5. The network access node (100) according to claim 4, wherein the first control message (502) is received in a physical uplink control channel, PUCCH, a medium access control element, MAC CE, or radio resource control, RRC, signaling.

6. A network access node (100) according to any of claims 1 to 3, further being adapted to:

a second control message (504) is sent to the client device (300), wherein the second control message (504) indicates transmission of DMRS according to the second DMRS pattern.

7. The network access node (100) of claim 6, wherein the second control message (504) is sent in a physical downlink control channel, PDCCH, MAC CE, or RRC signaling.

8. The network access node (100) of claim 7, wherein the second control message (504) is an indicator bit, wherein a "1" value of the indicator bit indicates that DMRS is transmitted according to the second DMRS pattern, and wherein a "0" value of the indicator bit indicates that DMRS is transmitted according to the first DMRS pattern.

9. A client device (300) for a wireless communication system (500), the client device (300) being configured to:

receiving a DMRS from a network access node (100) according to a first demodulation reference signal, DMRS, pattern in a wireless channel;

upon determining that the delay spread of the wireless channel exceeds the cyclic prefix length of the first DMRS pattern, transmitting a first control message (502) to the network access node (100), wherein the first control message (502) indicates that the delay spread of the wireless channel exceeds the cyclic prefix length;

-receiving a second control message (504) from the network access node (100), wherein the second control message (504) indicates that DMRS is transmitted according to a second DMRS pattern, wherein the second DMRS pattern is formed by the first DMRS pattern, the second DMRS pattern has one or more empty resource elements associated with the DMRS, wherein transmissions are not scheduled on the empty resource elements of the second DMRS pattern, resource elements are nulled in OFDM symbols carrying the DMRS pattern, and the DMRS pattern of the second DMRS pattern forms a comb structure;

-receiving DMRS from the network access node (100) according to the second DMRS pattern.

10. The client device (300) of claim 9, wherein the second DMRS pattern is DMRS configuration type 1, and wherein resource elements of antenna ports 0/1/4/5 or antenna ports 2/3/6/7 are nulled.

11. The client device (300) of claim 9, wherein the second DMRS pattern is DMRS configuration type 2, and wherein at least resource elements of antenna ports 0/1/6/7, 2/3/8/9, or 4/5/10/11 are nulled.

12. The client device (300) according to any of claims 9 to 11, wherein the first control message (502) is sent in a physical uplink control channel, PUCCH, a medium access control unit, MAC CE, or radio resource control, RRC, signaling.

13. The client device (300) according to any of claims 9 to 11, wherein the second control message (504) is received in PDCCH, MAC CE or RRC signaling.

14. The client device (300) of any of claims 9-11, wherein the second control message (504) is an indication bit, wherein a "1" of the indication bit indicates transmission of DMRS according to the second DMRS pattern and a "0" of the indication bit indicates transmission of DMRS according to the first DMRS pattern.

15. A method (200) for a network access node (100), the method (200) comprising:

transmitting (202) a DMRS to a client device (300) according to a first demodulation reference signal, DMRS, pattern in a wireless channel;

upon determining (204) that the delay spread of the wireless channel exceeds the cyclic prefix length of the first DMRS pattern, obtaining a second DMRS pattern formed by the first DMRS pattern, the second DMRS pattern having one or more null resource elements associated with a DMRS, wherein transmissions are not scheduled on the null resource elements of the second DMRS pattern, the resource elements are nulled in OFDM symbols bearing the DMRS pattern, and the DMRS pattern of the second DMRS pattern forms a comb structure;

-transmitting (206) DMRS to the client device (300) according to the second DMRS pattern.

16. A method (400) for a client device (300), the method (400) comprising:

-receiving (402) a DMRS from a network access node (100) according to a first demodulation reference signal, DMRS, pattern in a wireless channel;

upon determining (404) that the delay spread of the wireless channel exceeds the cyclic prefix length of the first DMRS pattern, transmitting a first control message (502) to the network access node (100), wherein the first control message (502) indicates that the delay spread of the wireless channel exceeds the cyclic prefix length;

-receiving (406) a second control message (504) from the network access node (100), wherein the second control message (504) indicates transmission of a DMRS according to a second DMRS pattern, wherein the second DMRS pattern is formed by the first DMRS pattern, the second DMRS pattern has one or more empty resource elements associated with the DMRS, wherein transmissions are not scheduled on the empty resource elements of the second DMRS pattern, the resource elements are nulled in OFDM symbols carrying the DMRS pattern, and the DMRS pattern of the second DMRS pattern forms a comb structure;

-receiving (408) DMRS from the network access node (100) according to the second DMRS pattern.

17. A computer readable storage medium storing a computer program, characterized in that the computer program when run on a computer performs the method according to claim 15 or 16.